Is there a way to sort messages by "newest first" and keep the setting as a default.

I'm searching around in the phpbb database to find out. In the meantime, you can sort the messages to see "newest first" by selecting from the dropdown box located at the bottom top of each topic.

I hope this will be a satisfactory fix. The only problem I foresee is for popular topics that have more than one page. The 'view most recent' works only for the page that is being viewed. You will still have to choose the last page of a topic in order to see the most recent post.